Several different centralizers exist on the market today wherein most of them have been designed for traditional casing and liner running and are not intended for drilling operations using the same.
When running casing or liner into a borehole the centralizers are used to improve cementing operations and also to reduce friction during such operations. If drilling with centralizers, the centralizer should also protect the pipe string from wear. Low rotational and running friction becomes increasingly important as horizontal displacement increases and drilling with liner and casing develop into a common technique.
Current technologies have a wide assortment of designs and components but the challenges of drilling with centralizers on the pipe string have not been properly considered during construction. This means that current equipment available on the market may cause friction forces between the casing and the borehole which are too high for a drilling application, even with the use of centralizers. The current equipment may also induce concern regarding the wear and integrity of a rotatable pipe string over time.
To be able to meet future well construction demands, there is a need for a centralizer which:                gives low rotational and sliding resistance;        protects the pipe string from external wear;        facilitates tripping, i.e. running a drill string into or pulling it out of a borehole;        can sustain long periods of rotation with flow; and        is robust enough to prevent possibility of junk in the borehole.        
The providers of centralizers also provide stop collars for locking the centralizers in place. Most of the current products are fastened to the pipe string by a number of bolts or screws through the stop collar body, biting into the surface of the pipe to lock the collars in place to prevent movement.
Recent testing has revealed that existing stop collars have weaknesses and might slide out of position downhole. This is particularly true when used in a liner- or casing-drilling application.
An extended amount of rotation is experienced during drilling operations with a casing or liner. The current means are not designed with drilling in mind and there is a high risk of the stop collars loosing their grip on the casing and starting to move. This causes the centralizers to shift position, which would disrupt the pipe string structure and also have a potential for damaging the pipe string integrity, e.g. with respect to burst and collapse, as the bolts of a loose stop collar can scrape into the outer surface of the pipe string at each rotation. A need exists for an improved design which can                secure a centraliser in place        reduce wear on end portion of centraliser        minimise friction between stop collar and centraliser        remove risk of reduced casing integrity from protruding bolts        